Optical semiconductor device

An optical semiconductor device comprising:

• a stripe-shaped ridge structure including a first-conductivity-type cladding layer, an active layer, and a second-conductivity-type first cladding layer which are sequentially laminated on a first-conductivity-type substrate;
• a buried layer which is buried on both side surfaces of the ridge structure to cover thereof;
• a second-conductivity-type second cladding layer and a second-conductivity-type contact layer which are sequentially laminated on a top of the ridge structure and a surface of the buried layer;
• a stripe-shaped mesa structure which is centered on the ridge structure and formed of a mesa reaching from the second-conductivity-type contact layer to the first-conductivity-type semiconductor substrate, both side surfaces of the mesa structure being formed by the mesa;
• a heat dissipation layer which is formed on a surface of the second-conductivity-type second cladding layer through a contact layer opening provided in the second-conductivity-type contact layer;
• a mesa protective film which is made of an insulating film and covers the both side surfaces of the mesa structure and both end portions of a surface of the second-conductivity-type contact layer;
• and
• a second-conductivity-type-side electrode which is electrically connected to the second-conductivity-type contact layer.

An optical semiconductor device comprising:

• a stripe-shaped ridge structure including a first-conductivity-type cladding layer, an active layer, and a second-conductivity-type first cladding layer which are sequentially laminated on a first-conductivity-type substrate;
• a buried layer which is buried on both side surfaces of the ridge structure to cover thereof;
• a second-conductivity-type second cladding layer and a second-conductivity-type contact layer which are sequentially laminated on a top of the ridge structure and a surface of the buried layer;
• a stripe-shaped mesa structure which is centered on the ridge structure and formed of a mesa reaching from the second-conductivity-type contact layer to the first-conductivity-type semiconductor substrate, both side surfaces of the mesa structure being formed by the mesa;
• a partial mesa protective film which is made of an insulating film and provided on both side surfaces of the mesa structure, one end portion of the partial mesa protective film reaching the first-conductivity-type semiconductor substrate exposed on the both side surfaces of the mesa structure, the other end portion of the partial mesa protective film covering at least the buried layer exposed on the both side surfaces of the mesa structure;
• and
• a second-conductivity-type-side electrode which is formed so as to cover a surface of the second-conductivity-type contact layer and to cover directly, at both end portions thereof, both side surfaces of the second-conductivity-type contact layer exposed on the both side surfaces of the mesa structure, and at least portions of the both side surfaces of the second-conductivity-type second cladding layer exposed on the both side surfaces of the mesa structure.